Presently, conventional eye drops are the standard means of delivering medicaments to the eye. This means of ophthalmic drug delivery, however, has numerous problems. For example, the average eye drop (approximately 50 micro liters) far exceeds the eye's capacity (7 micro liters in the pre-corneal tear film and a maximum of about 30 micro liters in the lower cul-de-sac) effectively destabilizing and stripping the natural tear film. This results in a brief period of massive over-dosage, which is quickly cleared by reflex lacrimation, blinking and nasolacrimal drainage, resulting in sub-therapeutic drug levels until the next medication application. This approach represents very inefficient pharmacokinetics. Far smaller volumes of medicament (approximately one tenth of a conventional drop) are desirable and are, in fact, retained by the eye and “bio-available” for a substantially longer time.
Attempts to prolong ocular contact time by various adaptations, such as the use of particulate suspensions, have led to other drawbacks including ocular irritation and excessively slow drug release. Ointments and gels, though providing prolonged contact time, create obvious visual disturbances.
Further, local irritations and toxicities often result from the regular use of eye drops. These situations vary widely depending on the pharmacologic agent, preservatives and other additives being used, but this is clearly a very non-physiologic and inefficient system of medication administration. Chronic use of eye drops for such conditions as glaucoma and prolonged infections and inflammations can, in fact, cause substantial morbidity. Additionally, serious and even fatal reactions to sympathomimetic and beta-adrenergic blocking agents have occurred as a result of systemic absorption of eye drops via nasolacrimal drainage.
Besides the above issues, there are a great many difficulties that patients experience with the mechanics of eye drop administration. Elderly patients, the largest group of eye drop users, often have hand-eye coordination problems, tremors or arthritis, affecting the hands and/or the cervical spine, making eye drop administration difficult if not impossible. Many users report that they have trouble keeping track of their regimens and often repeat doses or miss them entirely, suffering potential consequences in either event. Further, pediatric patients, often unable to comprehend the reasons and benefits behind the administration of eye medication, often fight such application, typically resulting in underdosing due to the patient's attempts to prevent the eye drops from being administered, or overdosing, as a result of the administrator's attempt to ensure that sufficient dosage is being applied.
Additionally, very few regular users of eye drops, in any age group, actually observe the ideal technique of administration, including tear sac compression, to minimize excretory loss and potential systemic absorption. It is sometimes difficult to tell if the drop was properly instilled. Direct application to the cornea can result in the drop “bouncing” from the eye with little or no benefit.
Regular eye drop users commonly report using several drops which “missed” the eye until they are sure they properly instilled the drop. Also, many eye drop bottles are fabricated in such a way that loss is unavoidable as soon as the dropper is tilted. Finally, a significant number of regular users put another drop or two in the eye “just to be sure”. All of the above represent needless waste of expensive medication (many glaucoma medications cost $70-$80 for a 5 ml bottle) and also increased the risk of side effects, while actually reducing the therapeutic benefit.
The ophthalmic literature is rife with references to the need for a better means of ophthalmic drug delivery. With an estimate of 25 million users of eye drops in the United States alone, the magnitude of the public health issue is considerable. Accordingly, a new means of ophthalmic drug delivery is needed.
The concept of “spraying” medicated solutions on to the eye is not a new one. A number of devices have been conceptualized and developed for this purpose. Various means of atomizing and propelling solutions including mechanical pumps, gas-propelled jets and pistons, etc. which have inherent drawbacks relating to difficulties with calibrating the flow velocity, volume and particle size of the emitted spray. See, for example, U.S. Pat. Nos. 3,170,462; 5,630,793; and 6,062,212.
It is hypothesized that the generated mist will expand and “therapeutically alter” but not significantly disrupt the physiologic tear film allowing for a more natural process in the transmission of therapeutic agents to the surface and the interior of the eye. A much smaller volume of solution can be administered below the blink and lacrimation thresholds, allowing for a prolonged time of application. The aggregate administration of a drug in thousands of 5-micron particles should significantly exceed that of a single eye drop, leading to greater concentrations of the drug (bioavailability). Furthermore, the surface tension of a standard drop is a barrier to “mixing” and tear film incorporation. This problem is expected to be avoided with micronebulization.
An additional benefit to mist administration of eye medications is the avoidance of dropper bottle contamination which commonly occurs from contact with the eyelid. In the professional office setting, this problem has led to many documented epidemics of viral keratoconjunctivitis. During medication administration via a dropper bottle to a patient with viral keratoconjunctivitis, the bottle tip may inadvertently touch the eye or eyelid of the affected patient, transferring the virus to the bottle tip. Subsequent medication administrations to other patients using the same dropper bottle transmits the virus to those patients.
Some of the beneficial features of an ophthalmic medication spray dispenser include the following: great ease of use; can be used in any “attitude” (i.e. with patient sitting, erect, lying down, head tilted back, etc.); abbreviated treatment cycle as compared to eye drop usage; improved bioavailability/efficacy; improved safety (reduced local and systemic side effects); improved sterility; increased compliance due to ease of use and “alert” systems; possibility of singular efficacy in the treatment of certain vision threatening infections; conservation of material (reduced volume, diminished waste/loss); and system (fixation target to help ensure proper application).
It would be beneficial to provide a system for applying the desired small amounts (7 to 10 micro liters) of optical medication, along with at least some of the above-listed beneficial features, while eliminating the drawbacks associated with previous means of drug delivery.